1. Field of the Invention
The present invention relates to a scroll compressor, and more particularly, to a scroll compressor in which an eccentric portion of a rotating shaft is connected to an orbiting wrap of an orbiting scroll in an overlapping manner.
2. Description of the Conventional Art
Generally, scroll compressors are widely used for compressing refrigerant in air conditioning equipment, by virtue of advantages of having a relatively higher compression ratio than other types of compressors and producing stable torque through a seamless sequence of suction, compression, discharge strokes of refrigerant.
Behavior characteristics of a scroll compressor are determined by the configuration of a fixed wrap of a fixed scroll and an orbiting wrap of an orbiting scroll. The fixed wrap and the orbiting wrap may have a certain shape, respectively, but in general, the fixed wrap and the orbiting wrap have an involute shape which makes them easily processable. The involute is a curve traced by an end of a string as it is unwound from a base circle with a certain radius. If the wraps have an involute shape, they have a uniform thickness and their volume changes at a constant rate. Thus, in order to obtain a sufficient compression ratio, the number of windings of the wraps should be increased. However, the scroll compressor becomes larger in size with an increasing number of windings of the wraps.
Typically, the orbiting scroll includes an end plate having a disk shape and the aforementioned orbiting wrap formed on one side of the end plate. A boss portion with a predetermined height is formed on the other side of the end plate where the orbiting wrap is not formed. A rotating shaft to be connected to a rotor of an electric motor portion is eccentrically connected to the boss portion to cause the orbiting scroll to orbit. With this configuration, the orbiting wrap can be formed over almost the whole area of the end plate, thereby reducing the diameter of the end plate for obtaining the same compression ratio. This configuration, however, axially separates the orbiting wrap and the boss portion from each other, and therefore, upon compression, the point of application of a repulsive force of refrigerant and the point of application of a reaction force for canceling out the repulsive force are axially separated from each other. Due to this, the repulsive force and the reaction force act as a couple while the compressor is running, causing the orbiting scroll to be tilted and therefore generating more vibration or noise.
To resolve this problem, there was disclosed a scroll compressor, like the scroll compressor (Korean Patent Registration No. 10-1059880) registered with the Korean Patent Office, in which the point of connection of the rotating shaft and the orbiting scroll is formed in the same plane as the orbiting wrap. This type of scroll compressor is capable of solving the tilting problem of the orbiting scroll because the point of application of a repulsive force of refrigerant and the point of application of a reaction force against the repulsive force act in opposite directions at the same height.
Well-known examples of scroll compressors in which an eccentric portion of a rotating shaft is connected to an orbiting wrap of an orbiting scroll in an overlapping manner include a top-mounted scroll compressor with a compressing portion located on top of an electric motor portion and a bottom-mounted scroll compressor with a compressing portion located under an electric motor portion.
Some top-mounted or bottom-mounted scroll compressors use a back pressure support system which supports the orbiting scroll by the back pressure created by bypassing an intermediate-pressure refrigerant to the back side of the orbiting scroll.
The above back pressure support system may not be able to support the orbiting scroll enough if the back pressure becomes lower due to a change in operating conditions or a high pressure in the compression chamber. As the orbiting scroll is connected to the eccentric portion of the rotating shaft with a fine gap, i.e., a bearing gap, interposed between them, the lack of back pressure may cause the orbiting scroll to wobble, so-called tilting. If this tilting goes beyond an allowable range, the refrigerant will leak from the compression chamber and hence the compression efficiency will drop or a collision will occur between the orbiting scroll and the rotating shaft, thus causing abrasion of bearings.